Method for drilling a well with emulsion drilling fluids

ABSTRACT

Oil in water emulsion drilling fluid properties are enhanced by incorporation thereinto of an alcohol such as glycerol or polycyclicpolyetherpolyol and salt.

This is a continuation-in-part of application Ser. No. 07/503,496, filedMar. 30, 1990, now abandoned which is a continuation-in-part ofapplication Ser. No. 07/377,740, filed July 17, 1989, now abandonedwhich is a division of application Ser. No. 07/167,768, filed Mar. 14,1988, now abandoned, and a continuation-in-part of application Ser. No.07/373,606, filed June 30, 1989, now abandoned, which is a division ofapplication Ser. No. 07/167,660, filed Mar. 14, 1988, now abandoned, anda continuation-in-part of application Ser. No. 07/353,195, filed May 12,1989, now abandoned, which is a division of application Ser. No.07/167,769, filed Mar. 14, 1988, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to water base drilling fluids. More particularly,the invention relates to water base drilling fluids having improvedcharacteristics which allow low temperature drilling operations, inhibitformation of gas hydrates which form at low temperatures and highpressures, reduce shale dispersion which results in improved wellborestability, reduce fluid loss, and are environmentally more safe.

Oil-in-water emulsion drilling fluids (or muds) generally comprisewater, oil, emulsifier, clays or polymers, and various treating agentswhich control the physical, chemical and/or rheological properties ofdrilling fluids in wellbores. Any type of aqueous drilling fluid can beconverted to an emulsion drilling fluid through the simple expedient ofadding the desired amount of oil and emulsifier. The drilling fluidserves to remove chips, cuttings and the like produced by a rotatingdrill bit from a wellbore by circulating the drilling fluid down fromthe surface of the well, through the drill string, and out throughopenings in the drill bit such that the drilling fluid is thencirculated upwardly in the annulus between the side of the wellbore andthe rotating drill string.

The selection of a drilling fluid is primarily dependent upon thegeological formation being drilled and the problems associated with suchformation. Principal concerns in selection of a drilling fluid aretemperature drilling conditions, formation of gas hydrates, shaledispersion, and drilling fluid loss and environmental requirements.Classically, temperature concerns associated with drilling oil/gas wellshave been associated with deep hot wells (>300° F.); however, for deepwater and/or Artic drilling low temperatures are a concern for twoprincipal reasons: (1) freezing of the mud due to low temperature,especially if the well must be shut in for long durations and (2) theformation of gas hydrates under low temperature and high pressureconditions after the influx of gas. The present invention provides adrilling fluid additive which overcomes these and other problems in theart as more particularly disclosed hereinafter.

DISCUSSION OF RELEVANT ART

Applicants are not aware of any art which, in their judgment as personsskilled in the art of drilling fluids, would anticipate or renderobvious the novel process and composition of the present invention.However, for the purpose of fully developing the background of theinvention, the following discussion is provided.

U.S. Pat. No. 4,063,603 (Rayborn) relates to a drilling fluid lubricant.While the patent is principally directed to the use of plastic beads asa drilling fluid lubricant, a list of other materials underconsideration as lubricating materials is provided which includesglycerines (Col. 2, line 3).

U.S. Pat. No. 4,508,628 (Walker et al) relates to oil base invertemulsion drilling fluids. In a list of temperature stabilizing additives(Col. 7, line 43) glycerine is mentioned. The presence of a salt, e.g.,NaCl (Col. 4, line 64), is described.

U.S. Pat. No. 4,478,612 (Diaz et al) describes a process for dryingsupercritical CO₂ with glycerol.

U.S. Pat. No. 4,597,779 (Diaz) discloses that the formation of hydratesin CO₂ is prevented by adding a polyhydric alcohol hydrate inhibitor.

U.S. Pat. No. 4,456,067 (Penner) discloses a process for inhibiting theformation of gas hydrates in producing gas wells, said gas hydrateinhibitor being a hydroxy-containing compound having less than about 10carbon atoms.

U.S. Pat. No. 3,738,437 (Scheureman) discloses the use of partiallyhydrolyzed polyarcylamide to avoid borehole instability.

SUMMARY OF THE INVENTION

The primary purpose of the present invention is to provide a drillingfluid, and process for the use thereof, which drilling fluid containsadditives which depress the freezing point of the drilling fluid toallow low temperature drilling operations, inhibit formation of gashydrates which form at low temperatures and high pressures, preventshale dispersion which results in improved wellbore stability, reducedrilling fluid loss thereby reducing amounts of other fluid lossadditives if any (e.g., gel-bentonite, carboxymethylcellulose, starch),and are environmentally more safe than oil base systems. Accordingly,the present invention is directed to an oil-in-alcohol emulsion waterbase drilling fluid comprising water, oil, emulsifier, clay or polymer,there being a sufficient amount of an alcohol such as glycerol orcyclicetherpolyol and, optionally, salt necessary to achieve the abovepurposes of the invention.

In addition, the present invention is directed to a method for drillinga well comprising rotating a drill string to cut a borehole into theearth; circulating water base drilling fluid through the drill stringand through the annulus between the drill string and the wall of theborehole checking the drilling fluid for evidence of any of thefollowing problems: freezing, gas hydrate formation, s hale dispersionand fluid loss; and adding oil-in-alcohol emulsion, optionally includingsalt, to the drilling fluid in an amount sufficient to overcome theabove identified problems. Further, the present invention provides amethod for drilling a well comprising determining whether the formationto be drilled will subject the drilling fluid to any of the followingproblems: freezing, gas hydrate formation, shale dispersion, and fluidloss; adding an oil-in-alcohol emulsion to the water base drillingfluid, optionally including salt, in an amount sufficient to overcomethe above identified problems; rotating a drill bit to cut a boreholeinto the earth; and circulating the drilling fluid through a drillstring and through an annulus between the drill string and the wall ofthe borehole.

Other purposes, distinctions over the art, advantages and features ofthe invention will be apparent to one skilled in the art upon review ofthe following.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates frictional coefficients for glycerol and glycerol/oilsurfactant emulsion.

DESCRIPTION OF PREFERRED EMBODIMENTS

Applicants have found that the use of an alcohol, preferably an acyclicpolyol such as glycerol, a monoalicyclicpolyol, or a cyclicetherpolyoland, optionally salt in an appropriate amount, as an oil-in-alcoholemulsion water base drilling fluid substantially depresses the freezingpoint of the drilling fluid to eliminate problems with low temperaturedrilling operations, inhibits formation of gas hydrates which form atlow temperatures and high pressures, prevents shale dispersion whichresults in improved wellbore stability, reduces drilling fluid lossthereby reducing amounts of other fluid loss additives if any (e.g.,gel-bentonite, carboxymethylcellulose, starch), and is environmentallysafe. Thus, according to the Applicant's method, the drill string isrotated to cut a borehole in the earth while circulating anoil-in-alcohol emulsion water base drilling fluid down through the drillstring and thence up the annular between the drill string and the wallof the borehole. While this is occurring, a driller preferably ischecking or observing the drilling fluid for evidence of the above notedproblems. Alternatively, the formation may be known in advance topresent certain problems, and the oil-in-alcohol emulsion water baseddrilling fluid may be utilized to overcome these problems.

In most instances, the applicable amount of oil-in-alcohol emulsion,optionally including salt, in the water base drilling fluid will bedetermined on a well-to-well basis. A concentration of alcohol in theoil-in-alcohol emulsion water base drilling fluid of from about 1 to 60,or preferably about 5 to 40 percent by weight and, optionally, of saltof from about 1 to 26, or preferably about 5 to 20 percent by weight,based on the total weight of the drilling fluid, will reduce thefreezing point of the drilling fluid by about 1 to 80 in °F. Aconcentration of from about 1 to 60, or preferably about 10 to 40percent by weight alcohol and, optionally, of from about 1 to 26, orpreferably about 5 to 26 percent by weight salt, based on the totalweight of the drilling fluid, will inhibit formation of gas hydrates. Aconcentration of from about 1 to 60, or preferably about 5 to 30 weightpercent alcohol and, optionally, of from about 1 to 26, or preferably toabout 5 to 20 percent by weight salt in the drilling fluid, based on thetotal weight of the drilling fluid, will prevent shale dispersion. Aconcentration of from about 1 to 60, or preferably about 5 to 40 weightpercent alcohol in the drilling fluid and, optionally, of salt of fromabout 1 to 26, or preferably about 5 to 15 weight percent, based on thetotal weight of the drilling fluid, will reduce fluid loss from thedrilling fluid through the wall of the wellbore.

Various inorganic salts are suitable for use with the invention,including but not limited to NaCl, NaBr, KCl, CaCl₂ and NaNO₃, amongwhich NaCl is preferred. A synergistic effect is experienced when such asalt is used with alcohol as a mud additive package, i.e., an effectgreater than the sum of the effects from salt and alcohol individually.

The oil employed to form the emulsion of the present invention may bemineral oil, crude oil, diesel fuel oil, kerosene, gas oil, or the like,and mixtures thereof.

In accordance with the present invention, any type of water basedrilling fluid can be converted to an emulsion drilling fluid throughthe expedient of adding the desired amount of oil, emulsifier(surfactants) and alcohol (e.g., glycerol). Emulsion drilling fluidsposses many advantages over regular drilling fluids, including but notlimited to, increases drilling rate, longer bit life, fewer round trips,less torque on pipe, less drag on pipe, and improved hole conditions.Emulsifiers (surfactants) preferred for use with the present inventionare diquarternary amines, alkylphenyl ethoxylates, alcohol ethoxylates,and amide ethoxylates. In accordance with the present invention it ishighly preferred to first make an emulsion of the oil, surfactant andalcohol (e.g., glycerol). This emulsion is then emulsified or mixed withwater. Emulsification preferably is accomplished through mechanicalagitation.

The alcohol of the present invention is preferably any water solublealcohol within the following groupings or mixtures thereof although anyalcohol of less than 8 hydroxyl groups and less than 16 carbon atoms issuitable. Hereinafter "poly" is used to mean two or more, "mono" is usedto mean one, "cyclic" is used to mean one or more rings, "ether" is usedto mean one or more ether linkages, PECP will mean either ofpolyetherpolycyclicpolyol, or polycyclicopolyetherpolyol.

A preferred class of alcohol components of this invention are acyclicpolyols. Among acyclic polyols, preferred are those having at least 3carbon atoms and 2 hydroxyl groups but no more than 80 carbon atoms and60 hydroxyl groups. More preferably, the acyclic polyols of theinvention have at least 9 carbon atoms and 5 hydroxyl groups but no morethan 50 carbon atoms and 40 hydroxyl groups.

Another preferred class of alcohol components of this invention aremonoalicylicpolyols. Among monoalicyclicpolyols, preferred are thosehaving 5 to 30 carbon atoms and 2 to 10 hydroxyl groups.

A most preferred class of alcohol components of this invention arecyclicetherolyols. Among cyclicetherpolyols, preferred are those havingat least 6 carbon atoms, at least 2 hydroxyl groups, and at least 2ether linkages, but no more than 1800 carbon atoms, 450 hydroxyl groups,and 600 ether linkages. Even more preferred are cyclicetherpolyolshaving at least 15 carbon atoms, 5 ether linkages, and at least 5hydroxyl groups, or at least 15 carbon atoms, at least 7 ether linkages,and at least 3 hydroxyl groups. Most preferred are cyclicetherpolyolshaving at least 18 carbon atoms, at least 6 hydroxyl groups, and atleast 6 ether linkages but preferably no more than 1200 carbon atoms,300 hydroxyl groups, and 400 ether linkages. Weight average molecularweights [defined infra] for the cyclicetherpolyols preferably range from1,000 to 30,000 and more preferably from 5,000 to 20,000. Among thecyclicetherpolyols, monocyclicdietherdiols are preferred andpolycyclicpolyetherpolyols are more preferred.

Nonlimiting examples include monomers, oligomers and telomers ofpolyhydric alcohols (or their precursors, or combinations thereof) suchas glycerol, telomers of glycerol such as diglycerols, triglycerols,tetraglycerols, pentaglycerols, and hexaglycerols, mixtures of glyceroland telomers of glycerol such as diglycerol and triglycerols, mixturesof telomers of glycerol, 1,5,6,9-decantetrol,1,2,4,5-cyclohexanetetramethanol, 1,2,4,7-heptanetetrol,1,2,3,5-heptanetetrol, 4,4-dimethyl-1,2,3-pentanetriol,1,3,4-cycloheptanetriol, 1,2,3-pentanetriol, 1,2,4-pentanetriol,2,3,4-pentanetriol, 1,1-cyclopentanediol, 1,2,3-cyclopentanetriol,1,2,3-hexantriol, 1,2,4-hexanetriol, 1,2,3,4-hexanetetrol,1,2,4-cyclohexanetriol, 1,2,5-cyclohexanetriol,1,2,3,4-cyclohexanetetrol, 1,2,3,5-cyclohexanetetrol, sorbitol,mannitol, and copolymers of ethylene glycol and propylene glycols withthe preceding alcohols.

Cyclicetherpolyols can be obtained, for example, by extraction fromsaline water byproduct streams arising from the manufacture of epoxyresins, e.g., by reaction of epichlorohydrin and bisphenol A asdescribed in U.S. Pat. Nos. 4,560,812 and 4,599,178, which areincorporated hereinto by reference thereto. The bottom stream obtainedfrom the distillation of synthetic and natural glycerine, usuallyreferred to as footstill bottoms, is also a convenient source ofpolycyclicpolyetherpolyols of the type referred to herein. In addition,a direct synthesis route is described hereinafter. The followingstructures are nonlimiting examples of this class of polyols. In orderto obtain cyclic ethers, the number of moles of water expelled must beat least equal to the number of moles of glycerol (or other polyhydric,at least trihydric, polyol) used in the reaction mixture. ##STR1## Instructures A through D, CIS and TRANS refer to the stereoisomerism ofthe carbon atoms marked by an asterisk. Structures A through D can alsobe called bis-hydroxymethyl 1,4-p-dioxanes.

Polycyclocpolyetherpolyols may in turn be prepared by polycondensationof compounds such a (A) through (E) supra in chemical processes whichare accompanied by significant expulsion of water molecules from thepolymerizing compounds. The number of ether linkages equals the numberof water molecules expelled. Taking (C) or (D) supra as the buildingunit, the lowest molecular weight structure containing two such units isStructure (II) infra, containing two terminal hydroxyl groups, and fiveether linkages. Structure (II) is formed by condensation from glycerolmolecules with the expulsion of five water molecules. ##STR2## Thisstructure is a di-cyclicpoly (or penta) etherdiol, and can be calleddi-bis-hydroxymethyl 1,4-p-dioxane.

Polycyclicpolyetherpolyols also can be formed by further condensation orpolycondensation of Structure (II) with itself, or with itself and withpolyhydric, at least trihydric, monomers, e.g., glycerol monomers.Dimerization of structure (II) with expulsion of one mole of wateryields: ##STR3## Copolycondensation of four structure (I) units withitself and with one polyhydric (at least trihydric) molecule, e.g., aglycerol molecule, can yield structure (IV) infra and its isomericequivalents: ##STR4## Analogous structures can be obtained fromstructures (I) (A), (I) B, and (I) E supra by polycondensation.Structures based on (E) supra will have five-membered rings.Spectroscopic techniques cannot conveniently distinguish between the 5or 6 membered rings.

Structures (IV) contains twelve ether linkages, three hydroxyl groups,and four six-membered cyclic diethers, and is formed by thepolycondensation of nine glycerol molecules by the expulsion of twelvewater molecules. The cyclic diether units and the polycondensed glycerolunits, or other polyhydric (at least trihydric) units, occur randomly inthe structure. Disregarding the order of occurrence, a general chemicalcomposition formula representative of all of these structures is:##STR5## where x≧1 and y≧0.

Preparation of cyclicetherpolyols for the practice of this invention canbe obtained by direct synthetic route. For example, starting withglycerol, chlorohydrin can be produced, which upon treatment with NaOHat elevated temperatures yields glycidol. This molecular structurecyclicizes at still higher temperature to yield bis hydroxymethyl1,4-p-dioxane. ##STR6## To make the higher molecular weight componentsfrom bis hydroxymethyl-1,4 p-dioxane and its isomers (I) (A-E) supra,the cyclic dimer is heated with acid (e.g., sulfuric acid) or basic(e.g., sodium acetate) catalyst while maintaining low pressure tofacilitate continuous removal of the water being expelled during thecondensation process. The rate of dehydration increases with increasingtemperature, but excessive temperatures should be avoided to eliminatepolymerization to intractable mixtures. Also it is essential to maintainan oxygen-free atmosphere over the solution while the reaction proceedsto avoid excessive oxidation and carbonization. Temperatures in therange of 150° C. to 350° C. can be employed with pressures ranging fromsubatmospheric to several atmospheres. The vapor pressure of thewater-free organic mixture is reduced as the average molecular weightincreases by condensation. However, the formation of water increases thepressure of the reactive mixture, and allows easy removal by continuousdistillation of the produced water. The extent of polycondensation canbe monitored by measuring the weight of produced water. For best resultsthe moles of water expelled should be at least equal to the startingnumber of polyhydric (at least trihydric) moles, e.g., glycerol moles.In a preferred composition the number of moles expelled bypolycondensation should be between 20% and 70% greater than the numberof the polyhydric, or at least trihydric, moles of alcohol in thereacting mixture. For example, from a starting feed of 9000 grams ofglycerol, 2200 to 2900 grams of water can be removed during thepolycondensation process or about 24% to 32% of the initial glycerolweight.

The monomeric units which can enter into the polycondensation reactionsto yield desirable polyethercyclic polyols are alcohols containing atleast three hydroxyl groups per molecule of which at least two arevicinal. Thus, glycols of any molecular weight do not meet therequirements of this most preferred embodiment. On the other hand,triols are quite suitable. Examples are butane triols, such as 1,2,4butanetriol, pentane triols, such as 1,2,3 pentanetriol, etc. Animportant class of polyhydric alcohols with straight carbon chains andfour or more hydroxyl groups, called sugar alcohols, can also be used inpreparing additive formulations containing cyclic polyethers. Sorbitoland mannitol are two such well known polyhydric alcohols.

A monomer of the structure: ##STR7## will yield several structures, oneof which is illustrated by: ##STR8##

The R group may itself be a group containing hydroxymethyl groups, whichwould in turn increase the potential for intermolecular condensation byexpulsion of additional moles of water, and would increase the facilitywith which high molecular weight cyclic ether structures are obtained.

Examples of cyclicdietherpolyols can be obtained from trihydric alcoholswith more than three carbons such as the following: ##STR9##

The following monocyclicdietherdiols of pentanetriol are obtained fromStructure IX in accordance with the methods described supra: ##STR10##Both dimers (A) and (B) are obtained from Structure IX by reacting atcarbons 1 and 2. ##STR11## Both dimers (C) and (D) are obtained byreacting Structure (IX) at carbons 2 and 3. ##STR12## Dimers (E) and (F)are obtained from (IX) by reacting at 1,2 and at 2,3 positions. Furtherpolycondensation of the cyclicetherdiols supra will yieldpolycyclicpolyetherpolyols with structures which depend on whichhydroxyl groups are involved in the condensation reaction. For instance,reaction between Structures (X) A supra and (X) F supra will yield (XI)infra, a dicyclicpentaentaetherdiol of pentanetriol as follows.Obviously, a large number of possible polycondensed structures exist.##STR13##

The molecular weight of a typical composition which was found to provideexcellent properties in the drilling fluid of this invention uponaddition to a level of 2% w, had molecular weight parameters asdetermined infra. Number average molecular weight M_(n) is shown by thefollowing: ##EQU1## This is the average molecular weight obtained whenthe total weight of the sample is divided by the number of molecules inthe sample. This molecular weight determines the effect of the sample onthe osmotic pressure and hence, the effect of the sample on the freezingpoint or other colligative properties of the total mixture. This M_(w)valve represents GPC results expressed in terms of PEG numbers obtainedby using two Ultrahydrogel columns, a 250 angstroms column and a 120angstroms column connected in series using water as solvent at 30° C.

The weight average molecular weight was found to be: ##EQU2## Thismolecular weight, weighs molecules proportionally to their molecularweight in the averaging process; that is, the molecular weight M_(i), ismultiplied by the weight n_(i) M_(i) of material of that molecularweight rather than by the number of molecules. This type of averagereflects the effect of the sample on those properties which depend onthe size of the individual molecules, such as effectiveness in lightscattering, or ability of the molecule to penetrate into small openings.Thus, a high M_(w) would be beneficial if penetration of the moleculesinto the interplanar structure of layered clays in the formation is tobe avoided. While the invention is not limited by this theory, it isbelieved that such a property minimizes the swelling of clay componentsin the wellbore, thereby improving wellbore stability.

The ratio M_(w) /M_(n) is also an indication of the spread orpolydispersity in the molecular weight of molecules present in thesample, and is by definition M_(w) ≧M_(n). This ratio is 8.6 for themost preferred formulation, PECP.

Most preferred samples of polycyclicpolyetherpolyols with beneficialeffects on the properties of drilling fluids have been found to haveM_(m) values in the order of about 150 to about 2000 and M_(w) values inthe order of 1500 to 12,000. The M_(n) and M_(w) values for POLS are130-145 and 700-875, respectively, but POLS (see below) is superior tomany other alcohols in carrying out the purposes of this invention.

Structural determination of mixtures using Mass Spectroscopy has yieldedx values (see structures V and VIII supra) of 1 to 4 in portions of thesample not exceeding 14 glycerol units, thus indicating that in asignificant portion of the sample x≧y/2, although the invention is notlimited to this theory. This procedure is limited with regard to themolecular weight of structures that it can determine, to molecules withabout 50 carbon atoms.

In accordance with a highly preferred embodiment of the invention,polycyclicpolyetherpolyols having superior characteristics are producedby thermal condensation of glycerol in distillation apparatus underconditions which allow water to be removed overhead, but not substantialamounts of glycerol or its dimers or trimers. A catalyst is required,preferably an alkali metal hydroxide, more preferably sodium hydroxide,in a preferred concentration of 0.5-1.5 percent by weight of thereaction mixture, and preferably including an alkali metal acetate, morepreferably sodium acetate, in like or smaller amounts.

The mixture is heated, preferably between 150 and 350 mm Hg and freewater is distilled off continuously, allowing the equilibrium limitedreaction to proceed further and to completion. The glycerol will thenbegin to rise in temperature to about 210°-230° C. at 120-180 mm Hg, atwhich temperature the mixture refluxes, indicating the onset of

The mixture is heated, preferably between 150 and 350 mm Hg and freewater is distilled off continuously, allowing the equilibrium limitedreaction to proceed further and to completion. The glycerol will thenbegin to rise in temperature to about 210°-230° C. at 120-180 mm Hg, atwhich temperature the mixture refluxes, indicating the onset ofreactions which produce water by condensation of the glycerol. Bymaintaining the pressure at up to 180 mm Hg, the glycerol, which mayvolatilize along with the water, is condensed in an overhead condensor,and preferably cooled by a coolant. The glycerol and its linear andcyclic dimers which form in the course of the volatilization process,are condensed and refluxed to the reacting mixture. Gradually theprocedure results in an increase in the boiling point of the mixture,brought about by the continuous removal of water of condensation and bythe increase of the molecular weight of the mixture.

As the degree of polymerization increases, and the water removed fromthe glycerol feed increases, the pressure over the mixture is graduallydecreased externally, either in a continuous, preferably gradual mode,or at selected reaction temperatures. For example, it is possible toreduce the pressure to 120 mm Hg when the mixture reaches 250° C. at apressure of 180 mm Hg. Alternatively, it is possible to control thepressure to diminish gradually by a known mechanical means.

The preferred way to achieve extensive dehydration without undesirablecrosslinking and gelation of the polycyclicpolyetherpolyols is by theaddition of small amounts of glycerol, at a later stage of the reaction,for example, when the reaction medium temperature has reached 270°-280°C. at a pressure of 50-100 mm Hg, preferably 60-90 mm Hg. Upon additionof 2-6 percent by weight of glycerol, basis final weight of glyceroladded, at a point after removal, for example, of 0.8 moles of water permole of glycerol, a drop in the temperature of the reaction mixtureoccurs, the drop being several degrees Centigrade or Fahrenheit. Thedrop is caused by the lower temperature of the glycerol being added, butmore importantly indicates the endothermic nature of the reactionbetween glycerol molecules, or between glycerol molecules and addedglycerol molecules, or between added glycerol molecules with reactivesites in the polymerizing mixture. For better effectiveness, theglycerol may be presaturated with alkaline metal hydroxide, e.g., sodiumhydroxide.

Upon continued input of heat from an external source, the temperature ofthe reacting mixture rises to the previous highest level, or to a higherlevel, or to a somewhat lower level than a first high temperature,depending upon the molecular weight distribution ofpolycyclicpolyetherpolyols in the mixture. This procedure of incrementalglycerol addition can be repeated a number of times, three being aconvenient number. With three additions of glycerol the experimentalreaction time between onset of reaction and its completion usually takes5-10 hours depending on the temperature and pressure of additions andthe amount of glycerol added each time. As the reaction approaches 85percent completion it is suitable to combine glycerol additions withfurther reductions of pressure, going down to b 30 mm Hg or even lower.As the reaction approaches completion, it turns from being highlyendothermic to being thermally neutral, and at a dehydration approachingand exceeding 1.2 moles of water per mole of glycerol, it can becomeexothermic. This is a reflection of the propensity of the mixture toundergo rapid crosslinking of the complex polycyclicpolyetherpolyolstructures. In order to avoid the occurrence of such an undesirablecrosslinking reaction, it is preferred to buffer the reaction by addinga small amount of glycerol, for example, 0.3-0.9 percent or up to 1.5percent by weight total. Preferably there is added 0.5 percent by weightof glycerol at a selected time or preferably at a point where thereaction is 96 percent complete, after removal of 1.12-1.15 moles ofwater per mole of glycerol in the reaction medium.

It has been found that the addition of minor amounts of epoxy resins tothe reaction mixture are beneficial. Preferred epoxy resins arediglycidyl ethers, triglycidyl ethers, and tetraglycidyl ethers which,in the reacting glycerol medium, result in formation of higher molecularweight polycyclicpolyetherpolyols which substantially improve propertiesin connection with drilling fluid performance.Polycyclicpolyetherpolyols resulting from this process are characterizedby binodal molecular weight distribution, M_(w) in excess of 50,000,said M_(w) being determined in a three-column gel permeationchromatography, and being 0.5 to 10% w epoxy structures. Thepolycyclicpolyetherpolyols are further characterized by molecularstructures which are no more than 20% free of associated cyclicformations.

Experimental results show that the impact of using multifunctionalglycidyl ethers on the value of M_(n) and on the performance,particularly as regards swelling of clays when the invention is used asa drilling fluid additive, is truly significant. Thus, when using 3.0% wEpon 828 (difunctional glycidyl ether) and 3.0% w Epon 1031(tetrafunctional glycidyl ether) tradenames of Shell Oil Company, theM_(w) values are correspondingly 78,015 and 151,000, and the swellinginhibition is the highest with Epon 1031, with good performance on fluidloss and on dispersion. The immediately preceding M_(w) values areexpressed in terms of true molecular weight in units of Daltons by usingthree Ultrahydrogel columns, a Linear column, a 250 angstroms column anda 120 angstroms column in series, using water as the solvent at 30° C.

The effectiveness of adding a commercially available polyol mixture(herein referred to as POLS) and polyetherpolycyclipolyols (hereinreferred to as PECP) prepared by Shell Chemical Company to inhibitcuttings dispersion are hereinafter shown for different drilling fluidcombinations. The POLS sample tested herein was analyzed to be 46.8% wpropylene glycol with 16.6% w linear dimers, 17.5% w linear trimers,3.8% w linear tetramers, 3.2% w linear pentamers, and 0.88% w linearhexamers of propylene glycol, with less than 0.5% w cyclics, 11% w waterand 0.2 to 0.5% w Na+ and K+. A typical PECP sample tested was 0.16% wglycerol, 11.4% w p-dioxanes, 1.1% w cyclic trimers of glycerol, 4% wcyclic and dicyclic tetramers of glycerol, 2% w cyclic and dicyclicpentamers of glycerol, 2% w dicyclic and tricyclic hexamers of glycerol,2% w dicyclic and tricyclic heptamers of glycerol, 3% w dicyclic andtricyclic octamers of glycerol, 4% w dicyclic and tricyclic nonamers ofglycerol, 27% w polycyclicpolyetherpolyols having at least 30 carbonatoms and at least 2 cyclic ethers per molecule, 37.5% w water, and 0.5%NaCl. The results indicate that PECP in combination with oil andsurfactant is an effective inhibitor of cuttings dispersion. TypicallyPECP with oil and surfactant is more effective at inhibiting cuttingsdispersion than glycerol in combination with oil and surfactant.

Drilling fluid properties should be such as to promote safe and speedydrilling and completion of the well with the maximum productivecapacity. Use of emulsion drilling fluids of controlled propertiesrequires expenditure of large sums of money, and to carry out its roleproperly, the drilling fluid must be protected against the effects offreezing conditions, gas hydrate formation, shale dispersion and fluidloss. The use of alcohol/oil emulsion in a water base drilling fluid,optionally including salt, readily protects the drilling fluid againstfreezing conditions and gas hydrate formation by lowering the freezingpoint of the drilling fluid. With respect to shale dispersion and fluidloss, the use of alcohol/oil emulsion in a water base drilling fluid,optionally including salt, aids in deposition of an impermeable filtercake, and the filter cake in turn prevents fluid loss and shaledispersion. The filter cake performs its job primarily on the basis ofits impermeability to water. If the formation permeability and thefluid-loss properties of the mud are both high, large quantities offluid will flow through the wall cake and into the permeable formation,leaving a thick wall cake behind. This cake may become so thick as toseriously interfere with movement of the drill pipe when it is withdrawnand may even result in sticking the pipe. If a thick cake is formed overthe face of the producing formation, it may not become properly cleanedoff during the well completion process and will interfere with theproduction rate of the well. The fluid which passes into the formationmay also exercise an influence. When the drilling fluid is water basedand shales and clays which are susceptible to hydration are drilled, theuse of high fluid loss drilling fluid may result in swelling and heavingof the shale, slow drilling rates, stuck pipe, fishing jobs and evenloss of the hole. If the producing formation contains hydratable clays,the intrusion of water may result in swelling of the clay particleswithin the sandy formation and permanent loss of permeability withresulting impaired production rates. The additive package of the presentinvention readily solves such problems by increasing the impermeabilityof the filter cake to water, thus decreasing the fluid-loss propertiesof the drilling fluid.

The following examples are illustrative of the application of theprocess of the present invention and of the drilling fluid composition,and are not to be construed as limiting the scope thereof.

In Table 1 data are shown that indicate that the addition of glycerol,oil and surfactant enhances performance in terms of inhibiting cuttingsdispersion. Each of the components oil, surfactant, and glycerol wereadded separately to fresh water or fresh water with NaCl. To evaluatethe synergistic effects, the percent shale retained in fresh water wassubtracted from all of the other test solutions. To determine synergybetween oil, surfactant and glycerol the percent retained (minus percentretained in fresh water) of the glycerol/fresh water, oil/fresh waterand surfactant/fresh water were added together. This result is apredicted value of 4.9 percent retained. This is significantly less thanwhat was obtained when all three components were added into the sametest solution.

When salt was present it was found that the percent retained of theindividual components (glycerol, oil and surfactant) in fresh water(minus the percent retained in fresh water) plus NaCl in fresh water(minus the percent retained in fresh water) was 37.6 percent retained.This was significantly less than what was observed when all fourreagents were in the same test solution. These results suggest asynergistic action between the different additives being tested.

The results of the tests of Table 1 suggested that the combination ofthese additives was not only an improvement, but was synergistic interms of inhibiting shale dispersion. As a means of improving theemulsification of the additives an emulsion of oil, glycerol andsurfactant was made prior to adding to fresh or salt water. Thisemulsion was stable at room temperature for weeks. The effectiveness ofthis emulsion to inhibit cuttings dispersion is shown in Table 2.

The emulsion was tested for inhibition of cuttings dispersion (Table 2)of two shales. The results indicate that the emulsion is an effectiveinhibitor of cuttings dispersion and that a synergistic relationshipexists between the presence of glycerol and oil/surfactant.

                                      TABLE 1                                     __________________________________________________________________________    Synergy Between Oil.sup.1, Surfactant.sup.2, and Glycerol.sup.5                               percent retained                                                                  Experi-                                                                       mental                                                                            Predicted                                                                            Predicted                                                          minus                                                                             Oil.sup.1 +                                                                          NaCl.sup.3 + Oil.sup.1 +                                       Experi-                                                                           Fresh                                                                             Glycerol.sup.5 +                                                                     Glycerol.sup.5 +                               Green Canyon 12,535 Feet                                                                      mental                                                                            Water                                                                             Surfactant.sup.2                                                                     Surfactant.sup.2                               __________________________________________________________________________    Fresh Water.sup.6                                                                             2.5                                                           Fresh Water (10%v Glycerol)                                                                   4.0 1.5                                                       Fresh Water (10%v Oil.sup.1)                                                                  4.2 1.7                                                       Fresh Water (1%v Sur-                                                                         4.2 1.7                                                       factant.sup.2)                                                                Fresh Water (10%v Oil.sup.1 /                                                                 3.6 1.1                                                       0.1%v Surfactant.sup.2)                                                       Fresh Water (10%v Oil.sup.1 /1%v                                                              20.0                                                                              17.5                                                                              4.9                                                   Surfactant.sup.2 /10%v Glycerol.sup.5)                                        0.150 M.sup.4 NaCl.sup.3,6                                                                    35.2                                                                              32.7                                                      0.15 M.sup.4 NaCl.sup.3 (1%v Sur-                                                             63.2                                                                              60.7                                                      factant.sup.2)                                                                0.15 M.sup.4 NaCl.sup.3 (10%v Glycerol)                                                       50.7                                                                              48.2                                                      0.15 M.sup.4 NaCl.sup.3 (10%v Oil.sup.1)                                                      36.2                                                                              33.7                                                      0.15 M.sup.4 NaCl.sup.3 (10%v Oil.sup.1 /                                                     65.6                                                                              63.1                                                      1%v Surfactant.sup.2)                                                         0.15 M.sup.4 NaCl.sup.3 (10%v Oil.sup.1 /                                                     72.8                                                                              70.3       37.6                                           1%v Surfactant.sup.2 /10%v                                                    Glycerol.sup.5)                                                               __________________________________________________________________________     .sup.1 Mineral Oil.                                                           .sup.2 Ethoxylated tallow amine.                                              .sup.3 NaCl always refers to 0.15 M NaCl. Percentage of alcohols,             glycerols, and surfactants is always percent by volume.                       .sup.4 M means molar.                                                         .sup.5 The oil/surfactant/glycerol emulsions were at a ratio of 24/1/75       percent by volume.                                                            .sup.6 Fresh water without XC resulted in 2.1 percent retained; 0.15 M        NaCl without XC resulted in 32.4 percent retained.                            Percent volume (%v) is based on total volume of solution. Test fluids and     shale were hot rolled for 45 seconds at 150° F. After the shale        test solution mixture was hot rolled, the shale was sized over 10, 30, an     80 mesh screen and dried. The data are expressed as percent retained of       the original weight (2.5 gm).                                                 XC polymer, which is a water soluble polysaccharide sold under the trade      name "Kelzan XC" by Kelco Corp., was added to the fresh water and NaCl        test solutions (0.2 lb/bbl) for viscosity control. As a result, all of th     test solutions had an apparent viscosity of approximately 2.0 centipoise      as measured on a Fann 35A.                                               

                                      TABLE 2                                     __________________________________________________________________________    Effectiveness of Emulsified Oil.sup.1 /Surfactant.sup.2 /Glycerol.sup.5       Combination                                                                                   percent retained                                                                  Experi-                                                                       mental                                                                            Predicted                                                                            Predicted                                                          minus                                                                             Oil.sup.1 +                                                                          NaCl.sup.3 + Oil.sup.1 +                                       Experi-                                                                           Fresh                                                                             Glycerol.sup.5 +                                                                     Glycerol.sup.5 +                                               mental                                                                            Water                                                                             Surfactant.sup.2                                                                     Surfactant.sup.2                               __________________________________________________________________________    Green Canyon 12,535 Feet                                                      Fresh Water.sup.6                                                                             2.4                                                           Fresh Water (7.5%v Glycerol)                                                                  3.7 1.3                                                       Fresh Water (2.4%v Oil.sup.1)                                                                 2.7 0.3                                                       Fresh Water (0.1%v Sur-                                                                       2.6 0.2                                                       factant.sup.2)                                                                Fresh Water (2.4%v Oil.sup.1 /                                                                2.7 0.3                                                       0.1%v Surfactant.sup.2)                                                       Fresh Water (10%v Oil.sup.1 /                                                                 16.5                                                                              14.1                                                                              1.8                                                   Surfactant.sup.2 /Glycerol.sup.5)                                             0.15 M.sup.4 NaCl.sup.3,6                                                                     34.6                                                                              32.2                                                      0.15 M.sup.4 NaCl.sup.3 (7.5%v                                                                41.2                                                                              38.8                                                      Glycerol)                                                                     0.15 M.sup.4 NaCl.sup.3 (2.4%v Oil)                                                           35.0                                                                              32.6                                                      0.15 M.sup.4 NaCl.sup.3 (0.1%v Sur-                                                           33.8                                                                              31.4                                                      factant.sup.2)                                                                0.15 M.sup.4 NaCl.sup.3 (2.4%v Oil.sup.1 /                                                    36.0                                                                              33.6                                                      0.1%v Surfactant.sup.2 )                                                      0.15 M.sup.4 NaCl.sup.3 (10%v Oil.sup.1 /                                                     55.2                                                                              52.8       34.0                                           Surfactant.sup.2 /Glycerol.sup.5)                                             South Timbalier 7,605 Feet                                                    Fresh Water.sup.6                                                                             16.0                                                          Fresh Water (7.5%v Glycerol)                                                                  20.4                                                                              4.4                                                       Fresh Water (2.4%v Oil.sup.1)                                                                 17.2                                                                              1.2                                                       Fresh Water (0.1%v Sur-                                                                       17.5                                                                              1.5                                                       factant.sup.2)                                                                Fresh Water (2.4%v Oil.sup.1 /                                                                21.2                                                                              5.2                                                       0.1%v Surfactant.sup.2)                                                       Fresh Water (10%v Oil.sup.1 /0.1%v                                                            32.2                                                                              16.2                                                                              7.1                                                   Surfactant.sup.2 /Glycerol.sup.5)                                             0.15 M.sup.4 NaCl.sup.3,6                                                                     38.6                                                                              22.6                                                      0.15 M.sup.4 NaCl.sup.3 (7.5%v                                                                51.2                                                                              35.2                                                      Glycerol)                                                                     0.15 M.sup.4 NaCl.sup.3 (2.4%v Oil.sup.1)                                                     39.2                                                                              23.2                                                      0.15 M.sup.4 NaCl.sup.3 (0.1%v Sur-                                                           39.0                                                                              23.0                                                      factant.sup.2)                                                                0.15 M.sup.4 NaCl.sup.3 (2.4%v Oil.sup.1 /                                                    45.1                                                                              29.1                                                      0.1%v Surfactant.sup.2)                                                       0.15 M.sup.4 NaCl.sup.3 (10%v Oil.sup.1 /                                                     57.9                                                                              41.9       28.5                                           0.1%v Surfactant.sup.2 /Glycerol.sup.5)                                       __________________________________________________________________________     .sup.1 Mineral Oil.                                                           .sup.2 Ethoxylated tallow amine.                                              .sup.3 NaCl always refers to 0.15 M NaCl. Percentage of alcohols,             glycerols, and surfactants is always percent by volume.                       .sup.4 M means molar.                                                         .sup.5 The oil/surfactant/glycerol emulsions were at a ratio of 24/1/75       percent by volume.                                                            .sup.6 Fresh water without XC resulted in 2.1 percent retained; 0.15 M        NaCl without XC resulted in 32.4 percent retained.                            To evaluate the synergistic effects, the percent shale retained in fresh      water was subtracted from all of the other test solutions. To determine       synergy between oil, surfactant, and glycerol, the percent retained (minu     percent retained in fresh water) of the glycerol/fresh water, oil/fresh       water, and surfactant/fresh water were added together. This result is the     predicted value.                                                              This value is significantly less than what was obtained when all three        components were in the same test solution.                                    When salt was present it was found that the percent retained of the           individual components (glycerol, oil, and surfactant) in fresh water          (minus the percent retained in fresh water) plus NaCl in fresh water          (minus the percent retained in fresh water) represented the predicted         percent retained. This was significantly less than what was observed when     all four reagents were in the same test solution. These results suggest a     synergistic action between the different additives being tested.              Test fluids and shale were hot rolled for 45 seconds at 150° F.        After the shale test solution mixture was hot rolled, the shale was sized     over 10, 30, and 80 mesh screen and dried. The data are expressed as          percent retained of the original weight (2.5 gm). XC polymer, which is a      water soluble polysaccaharide sold under the trade name "Kelzan XC" by        Kelco Corp., was added to the fresh water and NaCl test solutions (0.2        lb/bbl) for viscosity control.                                                As a result, all of the test solutions had an apparent viscosity of           approximately 2.0 centipoise as measured on a Fann 35A.                  

                                      TABLE 2A                                    __________________________________________________________________________    Synergy Between Emulsified Oil.sup.1, Surfactant.sup.3, and PECP                               percent retained                                                                  Experi-                                                                       mental                                                                            Predicted                                                                           Predicted                                                           minus                                                                             Oil.sup.1 +                                                                         NaCl.sup.3 + Oil.sup.1 +                                        Experi-                                                                           Fresh                                                                             PECP +                                                                              PECP +                                                          mental                                                                            Water                                                                             Surfactant.sup.2                                                                    Surfactant.sup.2                               __________________________________________________________________________    Green Canyon 12,535 Feet                                                      Fresh Water      3.0                                                          Fresh Water (7.4%v PECP)                                                                       12.5                                                                              9.5                                                      Fresh Water (2.5%v Oil.sup.1)                                                                  3.5 0.5                                                      Fresh Water (0.1%v Sur-                                                                        4.0 1.0                                                      factant.sup.2)                                                                Fresh Water (10%v Oil.sup.1 /0.1%v                                                             38.9                                                                              35.9                                                                              11.0                                                 Surfactant.sup.2 /7.4%v PECP)                                                 Fresh Water (2.5%v Oil.sup.1 /                                                                 6.0 3.0                                                      0.1%v Surfactant.sup.2)                                                       0.15 M.sup.4 NaCl.sup.3                                                                        36.5                                                                              33.5                                                     0.15 M.sup.4 NaCl.sup.3 (0.1%v Sur-                                                            62.5                                                                              59.5                                                     factant.sup.2)                                                                0.15 M.sup.4 NaCl.sup.3 (2.5%v Oil.sup.1 /                                                     66.7                                                                              63.7                                                     0.1%v Surfactant.sup.2)                                                       0.15 M.sup.4 NaCl.sup.3 (10%v Oil.sup.1 /0.1%v                                                 86.6                                                                              83.6      44.5                                           Surfactant.sup.2 /7.4%v PECP)                                                  South Timbalier 7,605 Feet                                                   Fresh Water      14.6                                                         Fresh Water (7.4% PECP)                                                                        26.5                                                                              11.9                                                     Fresh Water (7.4%v Oil.sup.1)                                                                  15.0                                                                              0.4                                                      Fresh Water (0.1%v Sur-                                                                        19.0                                                                              4.4                                                      factant.sup.2)                                                                Fresh Water (2.5%v Oil.sup.1 /                                                                 22.3                                                                              7.7                                                      0.1%v Surfactant.sup.2)                                                       Fresh Water (10%v Oil.sup.1 /0.1%v                                                             58.3                                                                              43.7                                                                              16.7                                                 Surfactant.sup.2 /7.4%v PECP)                                                 0.15 M.sup.4 NaCl.sup.3                                                                        40.6                                                                              26.0                                                     0.15 M.sup.4 NaCl.sup.3 (7.4%v PECP)                                                           65.9                                                                              51.3                                                     0.15 M.sup.4 NaCl.sup.3 (2.5%v Oil.sup.1)                                                      41.3                                                                              26.7                                                     0.15 M.sup.4 NaCl.sup.3 (0.1%v Sur-                                                            42.3                                                                              27.7                                                     factant.sup.2)                                                                0.15 M.sup.4 NaCl.sup.3 (2.5%v Oil.sup.1 /                                                     50.3                                                                              35.7                                                     0.1%v Surfactant.sup.2)                                                       0.15 M.sup.4 NaCl.sup.3 (10%v Oil.sup.1 /0.1%v                                                 81.3                                                                              66.7      42.7                                           Surfactant.sup.2 /7.4%v PECP)                                                 Green Canyon 12,545 Feet                                                      Fresh Water      2.1                                                          Fresh Water (0.1%v Sur-                                                                        2.3 0.2                                                      factant.sup.2)                                                                Fresh Water (7.4%v PECP)                                                                       13.9                                                                              11.8                                                     Fresh Water (2.5%v Oil.sup.1)                                                                  2.3 0.2                                                      Fresh Water (2.5%v Oil.sup.1 /                                                                 5.4 3.3                                                      0.1%v Surfactant.sup.2)                                                       Fresh Water (10%v Oil.sup.1 /0.1%v                                                             40.3                                                                              38.2                                                                              12.2                                                 Surfactant.sup.2 /7.4%v PECP)                                                 0.15 M.sup.4 NaCl.sup.3                                                                        33.5                                                                              31.4                                                     0.15 M.sup.4 NaCl.sup.3 (7.4%v PECP)                                                           74.1                                                                              72.0                                                     0.15 M.sup.4 NaCl.sup.3 (2.5%v Oil.sup.1)                                                      31.0                                                                              28.9                                                     0.15 M.sup.4 NaCl.sup.3 (2.5%v Oil.sup.1 /                                                     65.3                                                                              63.2                                                     0.1%v Surfactant.sup.2)                                                       0.15 M.sup.4 NaCl.sup.3 (0.1%v Sur-                                                            60.2                                                                              58.1                                                     factant.sup.2)                                                                0.15 M.sup.4 NaCl.sup.3 (10%v Oil.sup.1 /0.1%v                                                 80.3                                                                              78.2      43.6                                           Surfactant.sup.2 /7.4%v PECP)                                                 __________________________________________________________________________     .sup.1 Mineral Oil.                                                           .sup.2 Ethoxylated tallow amine.                                              .sup.3 NaCl always refers to 0.15 M NaCl. Percentage of alcohols,             glycerols, and surfactants is always percent by volume.                       .sup.4 M means molar.                                                         Samples were hot rolled at 150° F. for 45 seconds.                     The oil, surfactant, and PECP were added percent by volume at a ratio of      25/1/74 by volume respectively.                                               The emulsion was added at 10%.                                           

In Table 3 different combinations of oil, alcohol, and salt were testedfor inhibition of cuttings dispersion of Pierre shale. The resultsindicate that the combination of alcohol, salt, and surfactantemulsified together are effective inhibitors of cuttings dispersion.Also shown is a direct comparison between PECP and glycerol incombination with surfactant and oil. The results clearly suggest thatPECP is superior to glycerol.

Table 4 provides freezing point depression data which indicate that theoil/glycerol/surfactant mixture lowers the freezing point of fresh waterand salt water. This result suggests that this emulsion can be used toprevent freezing of mud in cold environments. In addition, it indicatesthat this emulsion will reduce the probability of forming gas hydratesin the drilling fluid.

In Table 5 data are presented showing that the alcohol/oil/surfactantemulsion can be used in a mud formulation without severely altering theprimary rheological or fluid loss properties.

                  TABLE 3                                                         ______________________________________                                        Effectiveness of Different Systems in the Presence of NaCl                             Ap-                                                                           parent                                                                        Vis-  percent retained                                                        cosity                                                                              Time (Hours)                                                   Formulations                                                                             (cps)   18     45   145  200  300  450                             ______________________________________                                        Fresh Water/add-                                                                         2        8.0    0.2 --   --   --   --                              ed XC.sup.1 0.2 lb/bbl                                                        20% NaCl/added                                                                           2       92.5   85.3 57.5 45.2 22.3 --                              XC.sup.1 0.2 lb/bbl                                                           20% NaCl   1       91.6   84.7 58.2 44.3 23.1 --                              without XC                                                                    20% NaCl (10%                                                                            2       97.8   93.5 85.3 79.8 68.6 --                              Glycerol)                                                                     20% NaCl (5%                                                                             2       97.7   96.0 93.5 90.0 82.9 72.3                            PECP)                                                                         20% NaCl (10%                                                                            2       95.6   92.3 68.3 55.3 35.6 --                              Oil.sup.4 /Surfactant.sup.3)                                                  20% NaCl (10%                                                                            2       98.6   97.3 92.3 88.6 82.3 --                              (Oil.sup.4 /Surfactant.sup.3 /                                                Glycerol)                                                                     20% NaCl (2%                                                                             2       99.7   98.4 --   93.2 87.9 79.7                            (Oil.sup.4)/Sur-                                                              factant.sup.3 /PECP)                                                          ______________________________________                                         .sup.1 XC is a water soluble polymer including polysaccharides sold under     the trade name "Kelzan XC" by Kelco Corp.                                     .sup.2 Sized shale cuttings (6-10 mesh) are rolled in the test fluid for      15 seconds at 150° F. The shale test solution mixture is then size     over 10, 30 and 80 mesh screens. The amount retained on the screens is        added and the percent retained is calculated relative to the original         starting material (2.5 gm).                                                   .sup.3 Ethoxylated tallow amine.                                              .sup.4 Mineral oil.                                                           Oil/Surfactant/Glycerol = Glycerol (93%)/Oil (5.8%)/Surfactant (0.9%)         (v/v%).                                                                       Oil/Surfactant/PECP = PECP (95%)/Oil (4%)/Surfactant (1.0%) (v/v%).           Oil/Surfactant = 10% oil.sup.4 in water with 1% surfactant (v/v%).            All samples were hot rolled at 150° F. for the indicated amount of     time.                                                                         All mixtures were by percent by volume.                                  

                  TABLE 4                                                         ______________________________________                                        Freezing Point Data for Alcohol/Oil.sup.1 /Surfactant.sup.2 Emulsion                            Core Lab Temperature                                                            Glycerol PECP                                             Formulations        (in °F.)                                                                        (in °F.)                                  ______________________________________                                        20% NaCl            1.0      1.0                                              20% NaCl/10% Emulsion                                                                             -4.0     -3.0                                             20% NaCl/20% Emulsion                                                                             -10.0    -11.0                                            20% NaCl/30% Emulsion                                                                             -19.0    -20.0                                            20% NaCl/40% Emulsion                                                                             -25.0    -26.0                                            20% NaCl/50% Emulsion                                                                             -29.0    -30.0                                            Fresh Water         32.0     32.0                                             Fresh Water/10% Emulsion                                                                          29.0     28.5                                             Fresh Water/20% Emulsion                                                                          20.0     20.0                                             Fresh Water/30% Emulsion                                                                          11.5     12.0                                             Fresh Water/40% Emulsion                                                                          0.5      0.5                                              Fresh Water/50% Emulsion                                                                          -20.0    -19.0                                            ______________________________________                                         .sup.1 Mineral oil.                                                           .sup.2 Ethoxylated tallow amine.                                              Freezing point data were determined by the ASTM method 1177.                  20% NaCl is 20% salt by weight. This solution was mixed with the              oil/alcohol/surfactant emulsion by volume.                                    Emulsion = 93% alcohol/5.8% oil/0.9% surfactant.                         

                                      TABLE 5                                     __________________________________________________________________________    Seawater/Bentonite Mud Formulations                                                  PECP                Glycerol                                           Formulations                                                                         1   2   3   4   5   6   7   8   9   10  11  12  13  14                 __________________________________________________________________________    Mud Weight                                                                           16.0                                                                              16.0                                                                              16.0                                                                              16.0                                                                              16.0                                                                              16.0                                                                              16.0                                                                              16.0                                                                              16.0                                                                              16.0                                                                              16.0                                                                              16.0                                                                              16.0                                                                              16.0               (ppg)                                                                         Seawater                                                                             245.0                                                                             221.0                                                                             196.0                                                                             172.0                                                                             147.0                                                                             245.0                                                                             221.0                                                                             196.0                                                                             172.0                                                                             147.0                                                                             221.0                                                                             196.0                                                                             172.0                                                                             147.0              (mls)                                                                         Glycerol (%                0   10.0                                                                              20.0                                                                              30.0                                                                              40.0                               v/v Sea                                                                       Water)                                                                        Oil.sup. /PECP/                                                                      0   10.0                                                                              20.0                                                                              30.0                                                                              40.0                                                   Surfactant.sup.                                                               (% v/v                                                                        seawater.sup.⊕)                                                           Oil.sup. /                                     10.0                                                                              20.0                                                                              30.0                                                                              40.0               Glycerol/                                                                     Surfactant.sup.                                                               (% v/v                                                                        Seawater.sup.⊕)                                                           Bentonite                                                                            10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0               (gm)                                                                          Drill Solids                                                                         35.0                                                                              35.0                                                                              35.0                                                                              35.0                                                                              35.0                                                                              35.0                                                                              35.0                                                                              35.0                                                                              35.0                                                                              35.0                                                                              35.0                                                                              35.0                                                                              35.0                                                                              35.0               (gm)                                                                          Barite (gm)                                                                          367.0                                                                             368.0                                                                             369.0                                                                             369.0                                                                             370.0                                                                             367.0                                                                             360.0                                                                             354.0                                                                             347.0                                                                             340.0                                                                             368.0                                                                             369.0                                                                             369.0                                                                             370.0              Chrome Lig-                                                                          6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0                nosulfonate                                                                   (gm)                                                                          Carboxy-                                                                             1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0                methyl-                                                                       cellulose                                                                     (gm)                                                                          Resinx.sup.  (gm)                                                                    2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0                Hot Rolled                                                                    150° F. for                                                            16 hours                                                                      600 RPM                                                                              69.0                                                                              72.0                                                                              76.0                                                                              85.0                                                                              92.0                                                                              70.0                                                                              72.0                                                                              70.0                                                                              67.0                                                                              72.0                                                                              73.0                                                                              75.0                                                                              77.0                                                                              82.0               300 RPM                                                                              40.0                                                                              42.0                                                                              43.0                                                                              47.0                                                                              51.0                                                                              41.0                                                                              41.0                                                                              41.0                                                                              37.0                                                                              41.0                                                                              43.0                                                                              43.0                                                                              45.0                                                                              47.0               Plastic Vis-                                                                         29.0                                                                              30.0                                                                              33.0                                                                              38.0                                                                              41.0                                                                              29.0                                                                              31.0                                                                              29.0                                                                              30.0                                                                              31.0                                                                              30.0                                                                              32.0                                                                              32.0                                                                              35.0               cosity.sup.  (cps)                                                            Yield Point                                                                          11.0                                                                              12.0                                                                              10.0                                                                              9.0 10.0                                                                              12.0                                                                              10.0                                                                              12.0                                                                              7.0 10.0                                                                              13.0                                                                              11.0                                                                              13.0                                                                              12.0               (lb/100 ft.sup.2 )                                                            10-Second                                                                            4.0 3.0 4.0 3.0 4.0 3.0 3.0 2.0 3.0 2.0 3.0 2.0 3.0 3.0                Gel                                                                           (lb/100 ft.sup.2)                                                             10-Minute                                                                            15.0                                                                              14.0                                                                              12.0                                                                              14.0                                                                              16.0                                                                              14.0                                                                              15.0                                                                              9.0 5.0 6.0 12.0                                                                              10.0                                                                              12.0                                                                              13.0               Gel                                                                           (lb/100 ft.sup.2)                                                             API.sup..0.  Fluid                                                                   10.0                                                                              3.5 4.0 3.0 2.5 9.0 6.0 4.5 4.0 5.0 3.5 4.6 3.5 3.5                Loss (ml)                                                                     Cake Thick-                                                                          4.0 2.0 2.0 2.0 2.0 4.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0                ness (32 inch)                                                                __________________________________________________________________________     .sup. Mineral oil.                                                            .sup. Ethoxylated tallow amine.                                               .sup.⊕ Oil/alcohol/surfactant was mixed at a ratio of 5/94/1 percent      by volume.                                                                    .sup. Water soluble, heat stable, synthetically formulated resin used for     high temperature fluid loss sold under the trade name Resinex by MI           Drilling Fluid Company.                                                       .sup. Plastic viscosity, yield point and gel strengths were determined        with a Fann 35A following the procedures outlined in API RP 13B (Standard     Procedures of Field Testing Drilling Fluids).                                 .sup..0. Test for fluid loss using the API fluid loss test described in       Standard Procedures of Field Testing Drilling Fluid (FP 13B). Test for AP     fluid loss is described in the Standard Procedures of Field Testing           Drilling Fluid (RP 13B).                                                 

In FIG. 1 frictional coefficients were determined using the FalexLubricity Tester. Five pounds per barrel of bentonite were mixed infresh water. The pH was adjusted to 10.0 with NaOH. The suspension wasthen mixed with either glycerol or glycerol/oil/surfactant emulsion at10% or 20% by volume and hot rolled at 150° F. and 16 hours. The controlwas bentonite without an additive. Data for the control were obtainedonly at the 100 inch/pound direct load since a greater load resulted inshearing of the pin. The results suggest that theglycerol/oil/surfactant emulsion has greater lubricating capabilitiesthan glycerol alone. This indicates that this emulsion could be used indrilling operations to reduce torque and drag.

The foregoing description of the invention is merely intended to beexplanatory thereof, and various changes in the details of the describedmethod and apparatus may be made within the scope of the appended claimswithout departing from the spirit of the invention.

What is claimed is:
 1. A method for drilling a well, comprising:rotatinga drillstring to cut a borehole into the earth; circulating water basedrilling fluid through the drill string and through the annulus betweenthe drill string and the wall of the borehole; checking the drillingfluid or evidence of at least one problem of (a) freezing, (b) gashydrate formation, (c) shale dispersion, and (d) fluid loss; and addingan oil-in-alcohol emulsion to the drilling fluid in an amount sufficientto substantially prevent said at least one problem from occurring, saidalcohol being in a concentration of from about 1 to 60 weight percentbased on the total weight of the drilling fluid, and said alcohol beingselected from the group consisting of (1) an alcohol having less than 8hydroxyl groups and less than 16 carbon atoms, (2) an acyclic polyolhaving 3 to 80 carbon atoms and 2 to 60 hydroxyl groups; (3) amonoalicyclicpolyol having 5 to 30 carbon atoms and 2 to 10 hydroxylgroups; and (4) a cyclicetherpolyol having 6 to 1800 carbon atoms, 2 to450 hydroxyl groups, and 2 to 600 ether linkages.
 2. A method fordrilling a well, comprising:determining whether the formation to bedrilled will subject water base drilling fluid to at least one problemof (a) freezing, (b) gas hydrate formation, (c) shale dispersion, and(d) fluid loss; providing the drilling fluid with an oil-in-alcoholemulsion in an amount sufficient to substantially prevent said at leastone problem from occurring; rotating a drill string to cut a boreholeinto the earth; and circulating the drilling fluid through the drillstring and through the annulus between the drill string and the wall ofthe borehole, said alcohol being in a concentration of from about 1 to60 weight percent based on the total weight of the drilling fluid, andsaid alcohol being selected from the group consisting of (1) an alcoholhaving less than 8 hydroxyl groups and less than 16 carbon atoms, (2) anacyclic polyol having 3 to 80 carbon atoms and 2 to 60 hydroxyl groups;(3) a monoalicyclicpolyol having 5 to 30 carbon atoms and 2 to 10hydroxyl groups; and (4) a cyclic-etherpolyol having 6 to 1800 carbonatoms, 2 to 450 hydroxyl groups, and 2 to 600 ether linkages.
 3. Themethod of claim 1 or claim 2 wherein the cyclicetherpolyol is apolycyclicpolyetherpolyol which is characterized by binodal molecularweight distribution, M_(w) in excess of 50,000, said M_(w) beingdetermined in a three-column gel permeation chromatography, and being0.5 to 10% w epoxy structures.
 4. The method of claim 3 wherein thepolycyclicpolyetherpolyol is further characterized by molecularstructures which are no more than 20% free of associated cyclicformations.
 5. The method of claim 1 or claim 2 wherein the alcohol hasless than 8 hydroxyl groups and less than 16 carbon atoms.
 6. The methodof claim 1 or claim 2 wherein the alcohol is an acyclic polyol having 3to 80 carbon atoms and 2 to 60 hydroxyl groups.
 7. The method of claim 1or claim 2 wherein the alcohol is a monoalicyclic polyol having 5 to 30carbon atoms and 2 to 10 hydroxyl groups.
 8. The method of claim 1 orclaim 2 wherein the alcohol is a cyclicetherpolyol having 6 to 1800carbon atoms, 2 to 450 hydroxyl groups, and 12 to 600 ether linkages.